1. Field of the Invention
The present invention relates to a touch panel controller and manufacturing method thereof and more particularly to a capacitive touch panel controller having high voltage driving capability and manufactured by a process manufacturing a programmable non-volatile memory and a method manufacturing the same.
2. Description of the Related Art
After the world is overwhelmed by smart phones and tablet personal computers (PC), touch panels have become the most popular user interface. Among various types of touch panels, capacitive touch panels supporting multiple touches are the ones getting special attention and gradually promote the widespread penetration of large-size touch panels. Current capacitive touch panels are classified as mutual-capacitance touch panels and self-capacitance touch panels, and their difference lies in operation of the controllers mounted thereon. Under the circumstance of expanded application scope, increasingly complicated environment in operation and cost reduction, touch panel controllers must confront high-noise environment everywhere. Hence, how to suppress noise becomes one of the most critical subjects in developing the integrated circuits (IC) of touch panel controllers.
With reference to FIG. 9, a conventional capacitive touch panel controller has a MCU 71, a non-volatile memory 72, a capacitive detection circuit 73 and a functional circuit 74 (such as power on reset (POR), internal RC oscillator (IRC OSC), low voltage detection (LVD), static random access memory (SRAM)). The capacitive detection circuit 73 is connected to X-axis traces and Y-axis traces of the capacitive touch pane. If the conventional capacitive touch panel is a mutual-capacitance touch panel, the capacitive detection circuit 73 transmits a driving signal to each X-axis trace and each Y-axis trace serves to receive a sensing signal. If the conventional capacitive touch panel is a self-capacitance touch panel, the capacitive detection circuit 73 transmits a driving signal to one of the traces and the same trace receives a sensing signal. The signals transmitted from the capacitive detection circuit 73 to each trace is controlled by a transmission circuit composed of multiple transistors.
When the signals transmitted from the transmission circuit have a regular voltage, such as 3.3V±10% or 5.5V±10%, the signal-to-noise ratio (SNR) of the signals become worse when noise intensity received by each trace of the touch panel is higher because SNR is limited by an operating voltage. If the signals transmitted from the transmission circuit have a relatively high voltage, the SNR of the high-voltage signals is higher than the SNR of the signals having regular voltage. Ideally, the voltage used by the high-voltage transmission circuit is N times larger than the voltage used by the transmission circuit having regular voltage, and the SNR of the high-voltage transmission circuit is naturally N times larger than that of the transmission circuit having regular voltage. From the foregoing, if the transmission circuit of the controller transmits signals with higher voltage, noise withstanding capability of the controller and the SNR of received signals can be enhanced. The capacitive detection circuit 73 adopts the following approaches to transmit signals with higher voltage.
1. External Boost IC
With reference to FIG. 10, one of the approaches for increasing voltage of signals transmitted from the controller is to connect a boost IC 75 to an output terminal of the transmission circuit of the capacitive detection circuit 73 so that signals transmitted from the transmission circuit increase their voltage levels after passing through the boost IC 75 and are further transmitted to the traces of the touch panel. Although such approach certainly boosts the voltage level of the signals transmitted from the transmission circuit, the approach requiring an additional boost IC 75 is not optimal no matter if the size or the cost is concerned.
2. Add High-Voltage Element in the Controller or Fabricate the Controller IC Using High-Voltage Process Technology.
Since the controller IC contains a non-volatile memory, problems arising from process integration must be taken into account when the processes manufacturing the controller IC are selected. However, as far as current process technology of non-volatile memory is concerned, if a high-voltage process manufacturing a high-voltage element is integrated in a non-volatile memory process, several mask processes and photo-lithography processes in the high-voltage process. With reference to FIG. 11, a high-voltage transistor 76 fabricated with a standard high-voltage process is shown. As can be seen in FIG. 11, in contrast to elements using regular voltage, the high-voltage transistor requires a drain/source drift (D/S Drift) area and a P/NMOS voltage threshold (P/NMOS Vt) and the like to adjust a drain/source implant concentration and a threshold voltage of MOS.
Hence, if the high-voltage transistor is also fabricated during the manufacturing process of the non-volatile memory, the high-voltage process should be added in the current non-volatile memory process. To tackle the addition, not only four to seven additional masks and lithography processes should be added, but also the manufacturing cost inevitably builds up because the logic of masking operation and the complementary logic may not allow the non-volatile memory and the high-voltage element to commonly use the N/P Drift, HV P/NMOS Vt and the like.
From the foregoing, the approach using an additional boost IC to increase the voltage of the transmitted signals is hardly feasible because of the size and cost concern. The approach adding high-voltage transistor in the process manufacturing a non-volatile memory causes cost buildup for the sake of more mask processes and photo-lithography processes required, and the high-voltage transistor and the non-volatile memory may not be jointly operated due to the problem on the logic of masking operation and the complementary logic. However, to increase the SNR of the transmitted signals, a high-voltage driving approach is a must. A feasible technical solution with the manufacturing process efficiency, cost, and higher SNR and anti-interference capability taken into account needs to be further addressed.